Undated handout picture of an adult hybrid salamander. UC Davis researchers have discovered that an alien salamander, introduced from Texas 60 years ago, has hybridized with the endangered native California Tiger Salamander and the hybrids are doing terrible damage. They cannibalize the natives, cause their larvae to be trapped in drying pools, and kill off California Chorus frogs, California red-legged frogs, the California long-toed salamander.

Photo: Benjamin M. Fitzpatrick, University Of Tennessee

Undated handout picture of an adult hybrid salamander. UC Davis...

Image 2 of 2

Undated handout picture of a Barred Tiger Salamander larva. UC Davis researchers have discovered that an alien salamander, introduced from Texas 60 years ago, has hybridized with the endangered native California Tiger Salamander and the hybrids are doing terrible damage. They cannibalize the natives, cause their larvae to be trapped in drying pools, and kill off California Chorus frogs, California red-legged frogs, the California long-toed salamander.

As if it isn't enough that the California tiger salamander and other amphibian pond-dwellers are forced to fight for survival against overdevelopment and pollution in the state, along comes a predatory half-breed salamander to present another serious threat.

The trouble didn't come suddenly to the native tiger salamanders, those yellow-spotted creatures once abundant in the state's ponds and vernal pools.

Their problems began some 60 years ago - even before human development began seriously impinging on their habitats - when commercial bait sellers in California imported millions of alien Texas amphibians called barred tiger salamanders whose larvae, known as "waterdogs," made excellent bait for fishermen.

The adult barred salamanders, which look remarkably like their California cousins, soon began populating ponds all over Northern California. Harmless at first, Texas invaders quickly mated with the California natives and their hybridized descendants spread all over the state and have been flourishing ever since. They are imperiling frogs and newts and, above all, the original tiger salamander, according to a UC Davis biologist.

Ryan and her colleagues sampled the habitats and studied the genetics of all three salamander species in ponds and pools throughout varied areas of California, particularly the Salinas Valley, where the salamanders are abundant and their problems striking. The team also built artificial ponds in the valley to study the natives and hybrids more closely.

More than 20 generations of hybridization, she and her colleagues reported, have resulted in a host of negative effects. One negative effect is that the hybrid salamanders out-compete the tiny larvae of the native tiger salamanders for food. With little food, the native larvae's normal transformation into full-grown adults becomes delayed, making the less agile little ones easy prey to the hybrids for a longer period of time each season, the researchers reported.

Ryan also reported changes in the genes of the hybrids. In a series of experiments conducted in artificial ponds on the Davis campus, she found that the hybrids are delaying emerging from their larval stage for longer and longer periods. She also noted that the hybrids have grown much larger than even the largest native tiger salamanders. Their gaping jaws, in fact, have become wide enough to engulf smaller varieties of the natives as well as their larvae, Ryan found.

Other victims of the hybrid hordes include Pacific Chorus frogs, otherwise known as California tree frogs, that are known for their raspy nocturnal trills, and the California newt that mostly occupies the moist forests of the state's coast range.

The hybridized salamanders also pose a threat to the survival of the rare and tiny endangered Santa Cruz long-toed salamander, whose only known habitat is a watery mating swamp near Watsonville. The habitat made news nearly 40 years ago when it was threatened by a proposed trailer park. It was finally ordered preserved only after UC and Cabrillo College students and scientists mobilized to save it.

In the report this week, Ryan also warned that the threatened California red-legged frog is in greater danger from the spread of the predatory hybrid salamanders. .

Because of heavily sprawling urban development, the California tiger salamanders have long been listed as threatened throughout the state, but small populations in Sonoma County and near Santa Barbara are designated as endangered, which calls for even greater habitat protection.

Even so, the hybrids pose a conundrum in some ways, Ryan said in an e-mail.

"The hybrids are displacing the native threatened species and are therefore a threat," she said. "But in places where they already exist, should we protect them because they're part native?"